Combined acid alkylation and thermal cracking process

ABSTRACT

A combined acid alkylation and thermal cracking process utilizing preferably H3PO4/BF3 acid catalyst wherein propane and ethane previously unconverted in the alkylation process are converted to olefinic compounds such as ethylene and propylene which in turn can be alkylated preferably with isobutane so as to upgrade these previously less valuable components to highly valuable liquid fuel components.

United States Patent Wentzheimer Dec. 9, 1975 COMBINED ACID ALKYLATION AND 2,404,897 7/1946 Axe 260/683, THERMAL CRACKING PROCESS 2,460,303 2/1949 McAllister et al, H 260/68361 2,906,795 9/1959 Ballard el al. 260/683.6l

[75] Inventor: William W. Wentzheimer, Glen Primary ExaminerDe]bert E. Gantz [73] Assignee: Sun Oil Company of Pennsylvania, Crasanakis Phil d l hi P Attorney, Agent, or FirmGe0rge L. Church; Donald R. Johnson; Stanford M. Back [22] Filed: June 26, 1974 [21] Appl. No.: 483,170 [57] ABSTRACT A combined acid alkylation and thermal cracking pro- [52] US. Cl. 260/683. cess utilizing preferably a J a acid Catalyst [51} Int. Cl. C07C 3/54 herein prop ne an h ne previously unconverted [58] Field of Search, 260/683,44, 683,58, 68359, in the alkylation process are converted to olefinic 260/683.6l, 683.62, 683.48 compounds such as ethylene and propylene which in turn can be alkylated preferably with isobutane so as [56] References Cited to upgrade these previously less valuable components UNITED STATES PATENTS to highly valuable liquid fuel components. 2,285,785 6/1942 Seguy 260/683.6l 5 Claims, 2 Drawing Figures 0f 7' A/ 3 SUBUTAA/E pic-ya: Z M 48309551? IHEIPMAL A n CRACK/1V6 r'" 0 ill i F5506 6 80mm; /4 w fllfi lflrf PI! ,5, P900067 COMBINED ACID ALKYLATION AND THERMAL CRACKING PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved alkylation process. More particularly, it relates to the combination of olefin-alkylation and olefin production by thermal cracking of otherwise non-alkylation processes. More particularly it relates to thermal cracking of propane and lighter components of an alkylation effluent to produce olefinic compounds which can be recycled, alkylated and thereby upgraded.

2. Description of the Prior Art In the art of refining petroleum, olefinic hydrocarbon gases such as propene, butylenes, and butenes produced in catalytic cracking processes have been employed as feed to alkylation processes with isobutane as a means of fixing these gases into liquid products suitable for incorporation into motor fuel, rather than burning these olefinic components as fuel gas.

Utilizing H POJBF acid catalyst, it is possible also to alkylate ethylene and propylene as well as the olefins mentioned above; however, the amount of ethylene and propylene in refinery streams at present is usually too low to take advantage of the acid catalysts now available, such as H PO /BF, acid catalyst. Since ethane and propane are inert in the alkylation process and are usually removed in a depropanizer distillation zone, it would be desirable to utilize this stream in a way more economical and profitable to the refiner than as fuel gas.

SUMMARY OF THE INVENTION A system is now put forth to utilize this depropanizer overhead stream as feedstock to a standard ethane/propane cracking furnace wherein it may be converted to ethylene and propylene, among other desirable products such as thermal gasoline, and recycled to the olefin absorber section of a known alkylation process thereby increasing the amount of olefin chargeable to the alkylation zone so as to improve alkylate production in a given refinery.

More particularly, in an improved acid alkylation process wherein a. a hydrocarbon stream comprising pentane and lower boiling components is separated in an absorption separation zone into a first component being of essentially greater olefinic content than the second, by adsorption of the olefinic compounds present in the hydrocarbon stream by isobutane,

b. the combined isobutane and absorbed olefinic compounds are alkylated in an acid catalyzed alkylation zone to produce an alkylate product,

c. the alkylate product is split into a vapor and a liquid portion,

d. the vapor portion is compressed and distilled in a first distillation zone to remove a first overhead stream comprising propane and lower boiling unreacted compounds and an essentially propane-free bottom stream which is recycled to step (b),

e. the liquid portion is distilled in a second distillation zone to remove a second overhead stream comprising unreacted liquid absorbent and lower boiling hydrocarbons and an alkylate product stream,

f. the second overhead stream is recycled to step (a) and g. the alkylate product is removed the improvement now put forth comprises h. charging the first overhead stream of step (d) comprising propane and lower boiling unreacted compounds to a thermal cracking zone to produce an ethyleneand propylene-containing product stream,

i. recycling the ethylene and propylene product stream to the absorption-separation zone of (a) wherein these olefinic compounds are absorbed by the isobutane and j. charging this combined olefin and isobutane to the acid alkylation zone of step (b) thereby increasing the olefin feed to the acid alkylation zone and increasing the alkylate yield thereof.

Preferably the acid-alkylation process is catalyzed by H POJBF catalyst and the thermal cracking operation operates on a one-pass basis at a temperature in the range of 1500" to 1600F and a pressure of about 20-40 psig.

Among the advantages of such a system are the utilization of previously unloaded catalyst, increasing of the alkylate yield and upgrading of refinery gas components to liquid fuel components by utilizing the available isobutane and utilizing the C,s and C s available in a refinery without a gas plant but rather with an absorber which replaces the gas plant function.

These and other advantages will be more readily apparent upon review of the description of the drawing and the preferred embodiment which follows.

DESCRIPTION OF THE DRAWING AND THE PREFERRED EMBODIMENT FIG. 1 is a flow diagram of one embodiment of the invention.

FIG. 2 is a flow diagram of the preferred embodiment as simulated in the Example which follows this description. This embodiment differs from FIG. 1 in the addition of three more feed streams as shown as Feed B, Feed C and Feed D.

Referring to FIG. I, a pentane and lighter feed stream flows via line 1 to absorber 2 wherein it is contacted with isobutane which enters via line 3.

Non-absorbed components and a portion of the absorbent exit via line 4 while the combined isobutane and olefin stream is withdrawn via line 5 and charged to the reactor 6. The absorber can operate either in countercurrent flow, as shown and preferred, or in concurrent manner. The absorber is a vapor-liquid equilibrium stage process.

The alkylation reactions between the absorbed olefins and absorbent, such as isobutane take place in the alkylation reactor which operates at a temperature in the range of 30 to F, preferably 40 to 60F, a pressure in the range of 100 to 200 psig., preferably in the range of -140 psig., an isobutane to olefin ratio of 6/1 to 20/1, preferably 10/] to 14/1 and an acid/hydrocarbon ratio of 0.5/1 to 3/], preferably 0.8/1 to 1.2/1.

The reactor effluent is withdrawn via line 23 and separated preferably into a liquid and a vapor at separator of flash drum 24. The vapor portion is then compressed in compressor 25 into a liquid sent via lines 7, 8, 9 and 3 to the absorber 2. A portion of the stream in line 7 is taken off and sent to the depropanizer 15 wherein propane and lighter components are separated by distillation from the butanes and heavier components, the former being withdrawn via line 16 and the latter being withdrawn via line 17 and recycled to absorber 2 via lines 9 and 3.

Alternatively, vapor can be removed from the top of 5 reactor 6 and sent directly to compressor 25. This vapor-liquid separation is due to the flashing as a result of reactor auto refrigeration.

The liquid portion removed from separator 24 is charged via line 10 to debutanizer 11 wherein alkylate 10 product is separated by distillation and removed via line 12 while unreacted liquid absorbent such as isobutane is taken overhead via line 13 and recycled to absorber 2 via lines 9 and 3. Also, a side-cut can be taken via line 27 as product. 15

range of l5001600F and a pressure preferably in the range of 20-40 psig.

Effluent from thermal cracking zone 18 is removed via line 19 and charged to distillation zone 20 wherein ethylene and propylene are separated from thermal gasoline components formed in the cracking zone.

These gasoline components are removed via line 21 while the overhead propylene and ethylene are removed via line 22 and charged'to absorber 2 along with the feed in line 1.

FIG. 11 shows a flow diagram similar to FIG. I with the addition of Feed 8 via line 24 into alkylation charge line 5, Feed C into debutanizer 11 via line 25 and Feed D into debutanizer overhead line 13 via line 26. Whereas Feed A contains fractions lighter than propane, Feeds B, C and D contain various amounts of hydrocarbons boiling between propane and isopentane and including propane, propylene, n-butane, isobutane, butenes and isopentane. This embodiment is explained fully and demonstrated in the Example which follows.

EXAMPLE The process of this invention is demonstrated herein via material balance computer simulation. Tables 1 and 2 contain the material and energy balance showing the composition, temperature, pressure and flow rate of each stream as numbered in FIG. 11. Table 3 shows the alkylation operating conditions used and Table 4 shows the thermal cracking of ethane and propane as supplied by the Stanford Research lnstitutes Process Economics Program Report No. 29A Ethylene, Propylene."

As can be seen from Table 2, the stream in line 16, in previous operations would end up in fuel gas whereas in the present process it is converted to the products shown in line 19, particularly ethylene and propylene, which in turn are sent via absorber 2 and line 5 to the alkylation reactor 6 wherein 2.1 barrels of alkylate/barrel ethylene and 1.9 barrels alkylate/barrel propylene are formed causing a substantial upgrading of the previ- 30 ously fuel gas components and an increase in alkylate yield.

Table 1 Material Balance and Energy Balance for Feed and Product Streams Feed Product Line 12 Line 27 Line 21 Line 4 A B C D Alkylate Sidecut Gasoline Abs. Eff.

Components (mole frac.) Hydrogen 0.154 0.113 Methane 0.445 0.204 Ethane 0.229 0.005 0.039 Ethylene 0.129 0.001 0.030 Propane 0.009 0.008 0.123 0.035 0.120 0.033 Propylene 0.020 0.009 0.005 0.01 2 n-Butane 0.002 0.133 0.445 0.063 0.461 0.004 0.016 i-Butane 0.004 0.308 0.429 0.901 0.536 0.339 0.564 Butenes 0.003 0.534 i-Pentanes 0.006 0.008 0.004 0.019 0.002 i-Hexanes 0.341 0.159

i-Heptanes 0.044 i-Oetanes 0.4413

i-Nonanes 0.142 Conditions Temp'F 77 77 77 77 333 158 171 I14 Pressure pain 130 130 130 130 130 130 130 Dbl/hr. 435 86 1659 $61 383 12 MSCFfhr. 960 2588 Table 2 Material and Energy Balance for Intermediate Streams Intermediates Line No. 5 23 10 13 7 14 B 17 9 16 19 22 Components (mole Frac.) Hydrogen 0.002 0.001 0.005 0.005 0.005 0.024 0.231 0.236 Methane 0.016 0.017 0.001 0.049 0.049 0.049 0.001 0.214 0.294 0.300 Ethane 0.044 0.048 0.010 0.014 0.115 0.115 0.115 0.008 0.506 0.158 0.162 Ethylene 0.020 0.114 0.117 Propane 0.029 0.031 0.020 0.031 0.051 0.051 0.051 0.010 0.028 0.192 0.130 0.130 Propylene 0.006 0.019 0.019 nButane 0.044 0.048 0.055 0.008 0.035 0.035 0.035 0.046 0.035 i-Butane 0.783 0.765 0.782 0.946 0.735 0.736 0.736 0.935 0.926 0.063 0.042 0. 36

Butenes Table 2-continued Material and Energy Balance for intermediate Streams Intermediates Line No. 5 23 13 7 14 s 17 9 l6 I9 22 i-Pentanes 0.002 0.001 0.003 i-Hexanes 0.002 0.031 0.045 0.006 0.006 0.006 0.007 0.002 0.01 1 0.001 i-l-leptanes 0.003 0.006 i-Octanes 0.038 0.059 0.001 0.001 0.001 0.001 i-Nonanes 0.0 l 2 0.019 Conditions Temp. "F 50 113 138 I36 45 100 100 I82 117 4a 106 3 Pressure sia 130 136 130 130 30 195 195 195 130 195 130 bllhr. 4719 4343 3046 2l88 1319 69 1190 5113 MSCF/hr. 34s 2086 220 1 1 451 673 660 Table 3 I Alkylation Operating Conditions Condition Simulation Preferred Range Range Temp, "F. 50 40 60 100 Pressure, psig. 130 120 M0 100 200 rCJolefin l2 l0 i4 6 20 Acid/hydrocarbon" ll .8 1.2 0.5 3 Conversion/bbl Olefin Bbl iC, Bbl Alkylate Consumed Produced Ethylene 1. 2.1 Propylene l .4 1.9 Butylenes 1.1 1.8

"Acid Catalyst Used 1-11,i o,/sF,

overhead from the depropanizer and the third frac- Table 4 tlon comprising unalkylated isobutane 1s separated 30 from both the debutanizer and the depropanizer Them and recycled as absorbent to said absorption zone. Conditions the improvement which comprises Temp 1500 600 d. thermally crackrng said second fraction of step (c) Pressure, psig. 2o Wl'llCl'l comprises propane and lower boiling hydro- Eula 59 mole"will"! 35 carbons in a thermal cracking zone to produce 2 Products, mole/mole Ethane Hydrogen 093 product stream comprismg thermal gasolme, propgf 'i 1 ylene, ethylene, unconverted propane and lower gs: $13 boiling parafiins, glo ylera I 0.21 e. fractlonatmg said product stream of step (d) tc enna aso ine 0.2l 4O Conversion/mole Propane 9O mama/pm withdraw said thermal gasoline as a product of saw Products, mole/mole Propane process, and 5213 8;" n? f. recycling said propylene, ethylene, unconvertec Ema, propane and lower boiling paraffins from said frac Ethylene 0.89 tionating step (e) to said absorption zone in step Propylene 0.37 (a) Thermal Gasoline 0. l 8

"Bnis Ski! Report 29A as cited in previous text The invention claimed is:

l. in an l-l PQyBF catalyzed alkylation process wherein a. a hydrocarbon stream comprising pentane and lower boiling paraifins and olet'ms is separated in a liquid absorption zone to produce a liquid absorption stream containing a predominant portion of said olefins in said hydrocarbon stream, said liquid absorption stream being formed by passing isobutane as the absorbent in said zone,

b. the isobutane absorbent and absorbed olefins in said absorption stream are alkylated in said H,P0 'BF, catalyzed alkylation zone to produce an alkylate product,

c. the alkylation hydrocarbon phase is separated by distillation in a debutanizer and depropanizer into at least three fractions, the first fraction comprising said alkylate product is withdrawn from the debutanizer, the second fraction comprising propane and lower boiling hydrocarbons is removed as 2. The process of claim 1 wherein said alkylate hydrocarbon phase in step (c) is split into a vapor fractior and a liquid fraction, said vapor fraction being charger to a first distillation zone wherein a propane-ricl stream is separated from an isobutane bottom stream said liquid fraction being charged to a second distilla tion zone wherein said liquid fraction is separated intc an isobutane overhead stream, an alkylate product bot tom stream and a butane sidecut stream; said isobutann overhead stream and said isobutane bottom stream an recycled to step (a); said propane-rich stream is passer to step (d); and said alkylate product bottom stream and said butane sidecut stream are withdrawn as sepa rate products.

3. The process of claim 2 which further comprise charging at least three separate additional feed stream comprising hydrocarbons boiling between isopentan and propane and including isopentane, propylene, bu tenes, isobutane, n-butane, and propane into (1) sai alkylation zone, (2) said second distillation zone, an (3) said isobutane recycle stream.

4. The process of claim 3 wherein said thermal crack ing zone is a one-pass operation operating at a tempera 3,925,500 7 8 ture in the range of 1500 to 1600F and a pressure in to lF, a pressure in the range of I00 to 200 psig, and the range of 20-40 psig. isobutane to olefin ratio in the range of 6 to 20 and an 5. The process of claim 4 wherein the alkylation in acid to hydrocarbon ratio in the range of 0.5 to 3. step(b)takes place atatemperature in the range of 30 5 

1. IN AN H3PO4BF3 CATALYST ALKYLATION PROCESS WHEREIN A. A HYDROCARBON STREAM COMPRISING PENTANE AND LOWER BOILING PARAFFINS AND OLEFINS IS SEPARATED IN A LIQUID ABSORPTION ZONE TO PRODUCE A LIQUID ABSORPTION STREAM CONTAINING A PREDOMINANT PORTION OF SAID OLEFINS IN SAID HYDROCARBON STREAM, SAID LIQUID ABSORPTION STREAM BEING FORMED BY PASSING ISOBUTANE AS THE ABSORBENT IN SAID ZONE, B. THE ISOBUTANE ABSORBENT AND ABSORBED OLEFINS IN SAID ABSORPTION STREAM ARE ALKYLATED IN SAID H3PO4,BF3 CATALYST ALKYLATION ZONE TO PRODUCE AN ALKYLATE PRODUCT, C. THE ALKYLATION HYDROCARBON PHASE IS SEPARATED BY DISTILLATION IN A DEBUTANIZER AND DEPROPANIZER INTO AT LEAST DISTILLAFRACTIONS, THE FIRST FRACTION COMPRISING SAID ALKYLATE PRODUCT IS WITHDRAWN FROM THE DEBUTANIZER, THE SECOND FRACTION COMPRISING PROPANE AND LOWER BOILING HYDROCARBONS IS REMOVED AS OVERHEAD FROM THE DEPROPANIZER AND THE THIRD FRACTION COMPRISING UNALKYLATED ISOBUTANE IS SEPARATED FROM BOTH THE DEBUTANIZER AND THE DEPROPANIZER AND RECYCLED AS ABSORBENT TO SAID ABSORPTION ZONE, THE IMPROVEMENT WHICH COMPRISES D. THERMALLY CRACKING SAID SECOND FRACTION OF STEP (C) WHICH COMPRISES PROPANE AND LOWER BOILING HYDROCARBONS IN A THERMAL CRACKING ZONE TO PRODUCE A PRODUCT STREAM COMPRISING THERMAL GASOLINE, PROPYLENE, ETHYLENE, UNCONVERTED PROPANE AND LOWER BOILING PARAFFINS, E. FRACTIONATING SAID PRODUCT STREAM OF STEP (D) TO WITHDRAW SAID THERMAL GASOLINE AS A PRODUCT OF SAID PROCESS, AND F. RECYCLING SAID PROPYLENE, ETHYLENE, UNCONVERTED PROPANE AND LOWER BOILING PARAFFINS FROM SAID FRACTIONATING STEP (E) TO SAID ABSORPTION ZONE IN STEP (A).
 2. The process of claim 1 wherein said alkylate hydrocarbon phase in step (c) is split into a vapor fraction and a liquid fraction, said vapor fraction being charged to a first distillation zone wherein a propane-rich stream is separated from an isobutane bottom stream; said liquid fraction being charged to a second distillation zone wherein said liquid fraction is separated into an isobutane overhead stream, an alkylate product bottom stream and a butane sidecut stream; said isobutane overhead stream and said isobutane bottom stream are recycled to step (a); said propane-rich stream is passed to step (d); and said alkylate product bottom stream and said butane sidecut stream are withdrawn as separate products.
 3. The process of claim 2 which further comprises charging at least three separate additional feed streams comprising hydrocarbons boiling between isopentane and propane and including isopentane, propylene, butenes, isobutane, n-butane, and propane into (1) said alkylation zone, (2) said second distillation zone, and (3) said isobutane recycle stream.
 4. The process of claim 3 wherein said thermal cracking zone is a one-pass operation operating at a temperature in the range of 1500* to 1600*F and a pressure in the range of 20-40 psig.
 5. The process of claim 4 wherein the alkylation in step (b) takes place at a temperature in the range of 30* to 100*F, a pressure in the range of 100 to 200 psig, and isobutane to olefin ratio in the range of 6 to 20 and an acid to hydrocarbon ratio in the range of 0.5 to
 3. 